Using Gem 'wicked_pdf' to Generate PDF FIle in Rails

Ok, it ‘s turn for PDF file in Rails.
The wicked_pdf is the best gem I have seen for generating pdf file. It is powerful, versatile and flexible. It also provides the capability of generate PDF from HTML file. This is just what I want.
Thewicked_pdf utilizing the shell utility wkhtmltopdf to serve a PDF file to a user from HTML.
There are also many options which provides huge flexibility to users to customize the output PDF file.

Installation

put it in Gemfile

gem 'wicked_pdf'

Likewise, bundle install. Then, execute the initializer.

$rails generate wicked_pdf

It will create app/config/initializers/wicked_pdf.rb. Normally, nothing has to do with it if higher version of Rails was used. (My Rails version is 5)
Because wicked_pdf is a wrapper for wkhtmltopdf, you’ll need to install that in Gemfile, too.

gem 'wkhtmltopdf-binary'

Of course, then bundle install.

Usage

1.Put the code in the response_tosection of the controller. Like:

def show
  @orderdetails = @order.orderdetails.includes(:model, :size, :color)
  respond_to do |format|
    fn = "order_#{@order.po_number}_#{Time.now.strftime("%Y-%m-%d %H:%M:%S")}"
    format.pdf { render pdf: fn, disposition: 'attachment'}
  end
end

2.Copy the show.html.erb to a new file and rename it as show.pdf.erb.
3. Remove all the link_to tags in the file to prevent them from showing in the pdf file.
It’s done!
Further reading: How To Create PDFs in Rails

Using Gem 'to_spreadsheet' to Generate XLSX FIle in Rails

Now, let’s find out how to generate Excel file in Rails.

After searching many gems, I found that axlsx is a very well-designed for my purpose. However, it generates xlsx file by building up the components piece by piece. I need a quick solution which can generates a xlsx file from html file. Then I found a gem called to_spreadsheet that is totally full-filled my needs!

Actually, to_spreadsheet is a wrapper of axlsx. It simplifies the usage and allows us using the existing view template to generate xlsx file.

Installation

Put it in Gemfile.

gem 'to_spreadsheet'

Likewise, bundle install.

Usage

1.Put the code in the response_tosection of the controller. Like:

def show
  @orderdetails = @order.orderdetails.includes(:model, :size, :color)
    respond_to do |format|
    fn = "order_#{@order.po_number}_#{Time.now.strftime("%Y-%m-%d %H:%M:%S")}"

    format.xlsx { render xlsx: :show, filename: fn }
  end
end

2.Copy the show.html.erb to a new file and rename it as show.xlsx.erb.
3. Remove all the link_to tags in the file to prevent them from showing in the xlsx file.
4. Try to put the data you need to show in <table></table> block.

Done!

Using Service Objects in Rails

If you have many lines of code in your Models or Controllers, you might need to extract the logics out of them and wrap them up to Service Objects

They may be:

• A bunch of code called by many controllers.
• Dealing with output or input.
• A specific part of code containing domain knowledge.

Let us take the CSV file generation of the order details for example.

Create a New Directory ‘app/services’

First, let’s create a new directory ‘services’ under ‘app/’.

$cd app
$mkdir services
$cd services

Create a New File ‘app/services/document_service.rb’

Second, add a new file called ‘document_service.rb’.

Create a New Service Object called ‘DocumentService’

Third, move the code in private action query_to_csv of the orders_controller to the new service object. Now, we call this service object as DocumentService.

class DocumentService
  def initialize(order_id)
    @order_id = order_id
  end

  # Use ActiveRecord::Base.connection.exec_query to query db directly only once.
  def to_csv
    query_string = 'select a.po_number as "PO Number", c.name as "Model Name", d.name as Color,
        e.name as Size, b.price as Price, b.quantity as Quantity,
        (b.price*b.quantity) as "Total Amount"
      from orders a, orderdetails b, models c, colors d, sizes e
      where a.id = b.order_id and b.model_id=c.id and b.color_id=d.id and b.size_id=e.id and b.order_id=' + @order_id.to_s
    results = ActiveRecord::Base.connection.exec_query(query_string)
    CSV.generate(headers: true) do |csv|
      csv << results.columns
      results.rows.each do |row|
        csv << row
      end
    end
  end
end

Modify The Show Action

Four, modify the show action and delete private action query_to_csv.

def show
   :
   :
  format.csv { send_data DocumentService.new(@order.id).to_csv, filename: fn }
  end
end

That’s all! Now the order controller looks nicer and cleaner.

Further readings:

• 7 Patterns to Refactor Fat ActiveRecord Models

The "Includes" Magic in Rails

If there are many associated models needed to be retrieved during a query, it’s time to use ‘includes’ instead of nothing. It will increase your apps performance by reducing the number of queries to database.
Here is the scenario:

Order has_many Orderdetails

Without ‘includes’

The code:

@orderdetails = @order.orderdetails

It generates the log below.

Started GET “/orders/1” for ::1 at 2016-10-10 04:09:07 +0800
Processing by OrdersController#show as HTML
Parameters: {“id”=>”1”}
Order Load (0.3ms) SELECT “orders”.* FROM “orders” WHERE “orders”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Rendering orders/show.html.erb within layouts/application
Orderdetail Load (0.6ms) SELECT “orderdetails”.* FROM “orderdetails” WHERE “orderdetails”.”order_id” = ? ORDER BY model_id, size_id ASC [[“order_id”, 1]]
Model Load (0.4ms) SELECT “models”.* FROM “models” WHERE “models”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Size Load (0.4ms) SELECT “sizes”.* FROM “sizes” WHERE “sizes”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Color Load (0.6ms) SELECT “colors”.* FROM “colors” WHERE “colors”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 4], [“LIMIT”, 1]]
CACHE (0.0ms) SELECT “models”.* FROM “models” WHERE “models”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
CACHE (0.0ms) SELECT “sizes”.* FROM “sizes” WHERE “sizes”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Color Load (0.2ms) SELECT “colors”.* FROM “colors” WHERE “colors”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 2], [“LIMIT”, 1]]
CACHE (0.0ms) SELECT “models”.* FROM “models” WHERE “models”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Size Load (0.1ms) SELECT “sizes”.* FROM “sizes” WHERE “sizes”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 2], [“LIMIT”, 1]]
CACHE (0.0ms) SELECT “colors”.* FROM “colors” WHERE “colors”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 4], [“LIMIT”, 1]]
CACHE (0.0ms) SELECT “models”.* FROM “models” WHERE “models”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
CACHE (0.0ms) SELECT “sizes”.* FROM “sizes” WHERE “sizes”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 2], [“LIMIT”, 1]]
CACHE (0.0ms) SELECT “colors”.* FROM “colors” WHERE “colors”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 2], [“LIMIT”, 1]]
Rendered orders/show.html.erb within layouts/application (105.4ms)
Rendered common/_navbar.html.erb (1.1ms)
Completed 200 OK in 275ms (Views: 236.7ms | ActiveRecord: 5.1ms)

It takes 14 queries and 5.1ms.

With ‘includes’

The code:

@orderdetails = @order.orderdetails.includes(:model, :size, :color)

It generates the log below.

Started GET “/orders/1” for ::1 at 2016-10-10 14:26:43 +0800
ActiveRecord::SchemaMigration Load (0.2ms) SELECT “schema_migrations”.* FROM “schema_migrations”
Processing by OrdersController#show as HTML
Parameters: {“id”=>”1”}
Order Load (0.2ms) SELECT “orders”.* FROM “orders” WHERE “orders”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Rendering orders/show.html.erb within layouts/application
Orderdetail Load (0.2ms) SELECT “orderdetails”.* FROM “orderdetails” WHERE “orderdetails”.”order_id” = ? ORDER BY model_id, size_id ASC [[“order_id”, 1]]
Model Load (0.1ms) SELECT “models”.* FROM “models” WHERE “models”.”id” = 1
Size Load (0.2ms) SELECT “sizes”.* FROM “sizes” WHERE “sizes”.”id” IN (1, 2) ORDER BY name ASC
Color Load (0.2ms) SELECT “colors”.* FROM “colors” WHERE “colors”.”id” IN (4, 2) ORDER BY name ASC
Orderdetail Load (0.2ms) SELECT “orderdetails”.* FROM “orderdetails” WHERE “orderdetails”.”order_id” = ? ORDER BY model_id, size_id ASC [[“order_id”, 1]]
Rendered orders/show.html.erb within layouts/application (84.2ms)
Rendered common/_navbar.html.erb (1.9ms)
Completed 200 OK in 617ms (Views: 560.0ms | ActiveRecord: 3.4ms)

It takes 6 queries and 3.4ms.
The includes method can minimize the queries to the database. Rails generates a single query each time it need the associated model by default. The ‘includes’ method, however, aggregates the queries to the same associated model .
For example, If there are four order details belong to order id ‘1’, Rails generates 12 ( 4 records x 3 associated models ) queries by default. On the other hand, it only takes 3 queries by using the ‘includes’ method.

Conclusion

Add ‘includes’ method for the query with many associated models.

SQL Statement with Single or Double Quotes for PostgerSQL ?

Single Quotes or Double Quotes? That is a Question!

Consider a sql statement:

SELECT model AS 'Model Name' FROM orders

We usually write it in the format below in Ruby on Rails:

query_string = "SELECT model AS 'Model Name' FROM orders"

It works fine for SQLite and MySQL, but fails for PostgreSQL!

The root cause is that PostgreSQL only accepts double-quoted key words!

Solution: use double-quotes instead of single-quotes:

SELECT model AS "Model Name" FROM orders

In Rails, it should be:

query_string = 'SELECT model AS "Model Name" FROM orders'

Note that it turns to be single quotes for wrapping the whole query string.

Using Ruby CSV Library to Export CSV File in Rails Apps - send_data method and 'exec_query' Approach

N+1 Queries Problem

Since there are 4 relations (order, model, color, size) for model Orderdetail, it causes ‘N+1 Query’ problems for this scenario. Let’s take a look at the console log:

Started GET “/orders/1.csv” for ::1 at 2016-10-08 12:54:14 +0800
ActiveRecord::SchemaMigration Load (0.2ms) SELECT “schema_migrations”.* FROM “schema_migrations”
Processing by OrdersController#show as CSV
Parameters: {“id”=>”1”}
Order Load (0.2ms) SELECT “orders”.* FROM “orders” WHERE “orders”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Orderdetail Load (0.2ms) SELECT “orderdetails”.* FROM “orderdetails” WHERE “orderdetails”.”order_id” = ? ORDER BY model_id, size_id ASC [[“order_id”, 1]]
Order Load (0.1ms) SELECT “orders”.* FROM “orders” WHERE “orders”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Model Load (0.1ms) SELECT “models”.* FROM “models” WHERE “models”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Size Load (0.1ms) SELECT “sizes”.* FROM “sizes” WHERE “sizes”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Color Load (0.3ms) SELECT “colors”.* FROM “colors” WHERE “colors”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 4], [“LIMIT”, 1]]
Order Load (0.1ms) SELECT “orders”.* FROM “orders” WHERE “orders”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Model Load (0.1ms) SELECT “models”.* FROM “models” WHERE “models”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Size Load (0.1ms) SELECT “sizes”.* FROM “sizes” WHERE “sizes”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Color Load (0.1ms) SELECT “colors”.* FROM “colors” WHERE “colors”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 2], [“LIMIT”, 1]]
Order Load (0.1ms) SELECT “orders”.* FROM “orders” WHERE “orders”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Model Load (0.1ms) SELECT “models”.* FROM “models” WHERE “models”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Size Load (0.1ms) SELECT “sizes”.* FROM “sizes” WHERE “sizes”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 2], [“LIMIT”, 1]]
Color Load (0.2ms) SELECT “colors”.* FROM “colors” WHERE “colors”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 4], [“LIMIT”, 1]]
Order Load (0.1ms) SELECT “orders”.* FROM “orders” WHERE “orders”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Model Load (0.1ms) SELECT “models”.* FROM “models” WHERE “models”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
Size Load (0.1ms) SELECT “sizes”.* FROM “sizes” WHERE “sizes”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 2], [“LIMIT”, 1]]
Color Load (0.1ms) SELECT “colors”.* FROM “colors” WHERE “colors”.”id” = ? ORDER BY name ASC LIMIT ? [[“id”, 2], [“LIMIT”, 1]]
Rendering text template
Rendered text template (0.0ms)
Sent data order_1234_2016-10-08 12:54:14.csv (14.0ms)
Completed 200 OK in 149ms (Views: 13.8ms | ActiveRecord: 4.7ms)

There are four order details for order 1, it takes 19 queries for 4.7ms. We can conclude that:

query number = ( number of order details X 4 ) + 3

Thus, the more order details contained in one order, the more query time used.

Direct SQL Query

Is there a way to solve this problem? What if we just use one single query to get all the data we need? Here is my plan. I wrote a single SQL statement which can pull out all the data from the database:

select a.po_number as ‘PO Number’, c.name as ‘Model Name’,
d.name as ‘Color’, e.name as ‘Size’, b.price as ‘Price’, b.quantity as Quantity (b.price*b.quantity) as ‘Total Amount’
from orders a, orderdetails b, models c, colors d, sizes e
where a.id = b.order_id and b.model_id=c.id and b.color_id=d.id and b.size_id=e.id and b.order_id=a.id

I tested it through a standalone database client and it returned the correct result. Then, I called ‘“exec_query” method to do the one-query action in the orders controller. The class used is:

ActiveRecord::Base.connection.exec_query([query string])

The result set is an ActiveRecord::Result object and very easy to handle with. The header and values of the result set can be obtained by using the following methods:

# Get the column names of the result:
result.columns
# => ["id", "model", "color"]

# Get the record values of the result:
result.rows
# => [[1, "model_1", "color_1"],
      [2, "model_2", "color_2"],
      ...
     ]

All we need to do is to save the header and the values to the csv string. All these code was wrapped into a private action query_to_csv(). In action show, the csv string is passed into send_data which outputs the result to the file in csv format.

format.csv { send_data query_to_csv(@order.id), filename: fn }

It’s quite simple. Here is the code in the controller.
app/controllers/orders_controller.rb

class OrdersController < ApplicationController
    :
    :
  def show
    @orderdetails = @order.orderdetails
    add_breadcrumb @order.id, order_path

    respond_to do |format|
      format.html
      format.json
      fn = "order_#{@order.po_number}_#{Time.now.strftime("%Y-%m-%d %H:%M:%S")}.csv"
      # Send_data method and exec_query approach
      format.csv { send_data query_to_csv(@order.id), filename: fn }
    end
  end   

  private

  # Use ActiveRecord::Base.connection.exec_query to 
  # query db directly only once.
  def query_to_csv(order_id)
    query_string = 'select a.po_number as "PO Number", 
        c.name as "Model Name", d.name as Color,
        e.name as Size, b.price as Price, 
        b.quantity as Quantity,
        (b.price*b.quantity) as "Total Amount"
      from orders a, orderdetails b, models c, 
        colors d, sizes e
      where a.id = b.order_id and b.model_id=c.id and
        b.color_id=d.id and b.size_id=e.id and
        b.order_id=' + order_id.to_s
    results = ActiveRecord::Base.connection.exec_query(query_string)       
    CSV.generate(headers: true) do |csv|
      csv << results.columns
      results.rows.each do |row|
        csv << row
      end
    end
  end
end

Note that PostgreSQL Server only allow double quote for the sql statement. So I use single quote for quoting the whole query string and double quote for the item name with space in it. For example:

‘select a.po_number as “PO Number”…………….. ‘

That’s it!

Performance Improvement

Let’s take a look at the console log.

Started GET “/orders/1.csv” for ::1 at 2016-10-08 12:58:50 +0800
ActiveRecord::SchemaMigration Load (0.2ms) SELECT “schema_migrations”.* FROM “schema_migrations”
Processing by OrdersController#show as CSV
Parameters: {“id”=>”1”}
Order Load (0.2ms) SELECT “orders”.* FROM “orders” WHERE “orders”.”id” = ? LIMIT ? [[“id”, 1], [“LIMIT”, 1]]
(0.2ms) select a.po_number as ‘PO Number’, c.name as ‘Model Name’, d.name as ‘Color’, e.name as ‘Size’, b.price as ‘Price’, b.quantity as Quantity, (b.price*b.quantity) as ‘Total Amount’ from orders a, orderdetails b, models c, colors d, sizes ewhere a.id = b.order_id and b.model_id=c.id and b.color_id=d.id and b.size_id=e.id and b.order_id=1
Rendering text template
Rendered text template (0.0ms)
Sent data order_1234_2016-10-08 12:58:50.csv (4.5ms)
Completed 200 OK in 56ms (Views: 4.3ms | ActiveRecord: 1.3ms)

It takes 3 queries for 1.3ms! More than three times faster!
Note: the private action can be extracted as a Service Object. Please refer to this article.

First CHEF Solo Installation and 'Hello World'!

Hello World! My First Cookbook.

CHEF is a platform of deployment automation. It is one of the important tools for DevOps engineers.
This is the first time I install Chef in my Mac, trying to understand how it works. Here are the installation processes I documented according to this tutorial.

Perequisites

First, make sure all listed below have been installed in my Mac.

• git
• Oracle VM VirtualBox
• Vagrant -> https://www.vagrantup.com/downloads.html
• Chef DK -> https://downloads.chef.io/chef-dk/

Workstation installation

curl -L https://www.opscode.com/chef/install.sh | sudo bash

sudo gem install knife-solo

gem list

knife configure

Node Setup

Use Ubuntu virtual Box for virtual machine.

mkdir chef
cd chef
vagrant init ubuntu/trusty64

Edit Vagrantfile. Remove ‘#’ before the two lines below and save.

config.vm.network :private_network, ip: "192.168.33.10"
config.vm.network :forwarded_port, guest: 80, host: 8080

Start the Vagrant virtual machine

vagrant up

SSH Setup

Official documentation
Extra reading
This step is to setup the host name of the virtual machine. It writes the host data into the ssh configuration file in the local machine (not the virtual machine).

vagrant ssh-config —host hogege >> ~/.ssh/config

Now we can use ssh hogege to connect to the vagrant virtual machine.

ssh hogege

Chef site-cookbooks creation

knife solo init chef-repo
cd chef-repo
knife solo prepare hogege
$ bootstrapping Chef...

Create cookbook

knife cookbook create hello -o site-cookbooks/

WARN: This command is being deprecated in favor of `chef generate cookbook` and will soon return an error.
Please use `chef generate cookbook` instead of this command.
 at /Users/chaoyee/.rvm/gems/ruby-2.3.1@global/gems/chef-12.14.89/lib/chef/knife.rb:430:in `block in run_with_pretty_exceptions'
** Creating cookbook hello in /Users/chaoyee/chef/chef-repo/sitecookbooks
** Creating README for cookbook: hello
** Creating CHANGELOG for cookbook: hello
** Creating metadata for cookbook: hello

Add the line below to /site-cookbooks/hello/recipts/default.rb file

log "Hello World"

Edit chef-repo/nodes/hogege.json

{
  “run_list”:[
    “recipe[hello]”
  ] 
}

Start cooking!

knife solo cook hogege

Result:

Recipe: hello::default
  * log[Hello World] action write
Running handlers:
Running handlers complete
Chef Client finished, 1/1 resources updated in 01 seconds

It shows the log has been written to the virtual machine ‘hogege’.
Finally, remember to shutdown the virtual machine by typing:

vagrant halt

:-)

Using Ruby CSV Library to Export CSV File in Rails Apps - send_data method Approach

‘send_data’ method approach

As we mentioned in the previous article, there are two approaches to generate CSV file. Here is the other approach: ‘send_data’ method approach.
The ‘send_data’ method approach use ‘send_data’ method to export data directly to the CSV file in the controller. It does not use the template file, instead, the ‘to_csv’ method is created in the object model. The ‘to_csv’ method utilizes CSV commands to generate data. Then ‘send_data’ method use object.to_csvto export data to the CSV file.
Again, we need to require CSV library in application.rb
app/config/application.rb

require 'csv'  <== add this line
require 'rails/all'
  :

For example, I need a download button on the show page of the model Order. First, I have to add code to the show action of the order controller. ( Actually I manipulate @orderdetails is orders controller )
app/controllers/orders_controller.rb

def show
     :
     :
  respond_to do |format|
    format.html
    fn = "order_#{@order.po_number}_#{Time.now.strftime("%Y-%m-%d %H:%M:%S")}.csv"
    format.csv { send_data @orderdetails.to_csv, filename: fn }
  end
end

Second, a new method .to_csv should be added in Orderdetail model.
app/models/orderdetail.rb

class Orderdetail < ApplicationRecord
    :
    :
  def po_number
    self.order.po_number
  end

  def m_name
    self.model.name
  end

  def s_name
    self.size.name
  end

  def c_name
    self.color.name
  end

  def self.to_csv
    header = ['PO Number','Model Name', 'Size', 'Color', 'Price (USD)', 'Quantity', 'Total Amount']

    attributes = %w{ po_number model_name 
      size_name color_name price quantity 
      total_amount}

    CSV.generate(headers: true) do |csv|
      csv << header

      all.each do |orderdetail|
        csv << attributes.map{ |attr| orderdetail.send(attr) }
      end
    end  
  end
    :
    :  
end

Note that %w(aaa bbb) is a shortcut for [“aaa”, “bbb”]. Meaning it’s a notation to write an array of strings separated by spaces instead of commas and without quotes around them.
The CSV library generates data according to the attributesarray to the csvobject. Then pass it to the function who calls it ( here is the send_datamethod).
While typing the url below in the browser, it downloads the CSV file instantly.

http://localhost:3000/orders/1.csv

Here is the exported CSV file.
File name: order_1234_2016-10-05 23-38-27.csv

PO Number,Model Name,Size,Color,Price (USD),Quantity,Total
1234,PINEROLO AL SE 0.2 TIG welded Sora 18 Carbon/Alloy Fork,700C X 48CM,Gloss Red,365.42,106,38734.52
1234,PINEROLO AL SE 0.2 TIG welded Sora 18 Carbon/Alloy Fork,700C X 48CM,Gloss Black,365.42,2,730.84
1234,PINEROLO AL SE 0.2 TIG welded Sora 18 Carbon/Alloy Fork,700C X 50CM,Gloss Red,365.42,2,730.84
1234,PINEROLO AL SE 0.2 TIG welded Sora 18 Carbon/Alloy Fork,700C X 50CM,Gloss Black,365.42,2,730.84

The last step is to make a link somewhere in the order show page.
app/views/orders/show.html.erb

<%= link_to 'Export to CSV', order_path(@order, format: :csv) %>

Done!

Using Ruby CSV Library to Export CSV File in Rails Apps - Template Approach

When we need to export data to a file in CSV format, we don’t need an extra gem to do so. The standard ruby library has included this functionality. All we need is to require it in application.rb
app/config/application.rb

require 'csv'  <== add this line
require 'rails/all'
  :

Now, I need to have a download button on the show page of the model Order. First, I have to add code to the show action of the order controller.
At this point, there are two ways to do the job. One is template approach, the other is send_data method approach.
(send_data method approach is in another article: here )

Template Approach

Template approach using XXX.csv.erbas a template to generate data to CSV file. Utilization of CSV commands exists in the template file.
app/controllers/orders_controller.rb

def show
     :
     :
  respond_to do |format|
    format.html
    fn = "order_#{@order.po_number}_#{Time.now.strftime("%Y-%m-%d %H:%M:%S")}.csv"
    format.csv do
      headers['Content-Disposition'] = "attachment; filename =" + fn
      headers['Content-Type'] ||= 'text/csv'
    end
  end
end

Second, a new template file show.csv.erb should be added and written in CSV format.
app/views/orders/show.csv.erb

<%- headers = ['PO Number','Model Name', 'Size', 'Color', 'Price (USD)', 'Quantity', 'Total'] -%>
<%= CSV.generate_line headers -%>
<%- @orderdetails.each do |orderdetail| -%>
  <%= CSV.generate_line([
    orderdetail.order.po_number,
    orderdetail.model.name,
    orderdetail.size.name,
    orderdetail.color.name,
    orderdetail.price,
    orderdetail.quantity,
    orderdetail.total_amount
    ]) -%>
<%- end -%>

Note that <%- -%>prevents the app from generating a line break in the CSV file.
While typing the url below in the browser, it downloads the CSV file instantly.

http://localhost:3000/orders/1.csv

Here is the exported CSV file.
File name: order_1234_2016-10-05 23-38-27.csv

PO Number,Model Name,Size,Color,Price (USD),Quantity,Total
1234,PINEROLO AL SE 0.2 TIG welded Sora 18 Carbon/Alloy Fork,700C X 48CM,Gloss Red,365.42,106,38734.52
1234,PINEROLO AL SE 0.2 TIG welded Sora 18 Carbon/Alloy Fork,700C X 48CM,Gloss Black,365.42,2,730.84
1234,PINEROLO AL SE 0.2 TIG welded Sora 18 Carbon/Alloy Fork,700C X 50CM,Gloss Red,365.42,2,730.84
1234,PINEROLO AL SE 0.2 TIG welded Sora 18 Carbon/Alloy Fork,700C X 50CM,Gloss Black,365.42,2,730.84

The last step is to make a link somewhere in the order show page.
app/views/orders/show.html.erb

<%= link_to 'Export to CSV', order_path(@order, format: :csv) %>

Done!
By the way, there are excellent articles about Ruby CSV library, highly recommended!
A Guide to the Ruby CSV Library, Part I
A Guide to the Ruby CSV Library, Part II

Few Tips for Pagination in Rails Apps

When pagination is needed in Rails apps, I always use gem will_paginate. Because it is very simple and just requiring little effort to accomplish my tasks, gem will_paginate become one of my standard gems for every project.
It is simple, but it still need customization to fit my need. For example, the output is not very pretty. The look is not professional.

← Previous 1 2 Next →

---

With Bootstrap Style

What if we use Bootstrap Style to make it a better look? Sure, there is a gem integrates the Twitter Bootstrap pagination component with will_paginate. It is will_paginate-bootstrap.
As usual, add will_paginate-bootstrapin Gemfile:

gem 'will_paginate-bootstrap'

Prepare collection in controller.

def index
  @orders = Order.all.page(params[:page]).per_page(3)
end

Note that the new, shorter page() method is used. It is easier and more intuitive. Then add the line in view template (change @orders to your collection ):

<%= will_paginate(@orders, renderer: BootstrapPagination::Rails %>

---

Customize the ‘Previous’ and ‘Next’ Tabs

What if we need to replace these two tabs to a simpler way such as ‘<’ and ‘>’?
According to the API documentation, we can assign these options :previous_label and :next_label to the characters we prefer. Therefore, the code becomes:

<%= will_paginate(@orders, 
  renderer: BootstrapPagination::Rails, 
  previous_label: '<', 
  next_label: '>' 
%>

The result:

---

One More Thing: Helper Method

Note that there are many models shown with pagination. The code is duplicated in every view template. Once again, we need code refactoring. I make a helper method generate_pagination in application_helper.rb :

def generate_pagination(object_handled)
  object_paginated = will_paginate(
    object_handled, 
    renderer: BootstrapPagination::Rails,
    previous_label: '<', next_label: '>')
  object_paginated.html_safe if object_paginated
end

Note that the object_paginated is nil (no pagination shown) while there is only one page in the view. A check of object_paginated is necessary for preventing error.
And the view template:

<%= generate_pagination(@orders) %>

That’s it!

Making breadcrumbs navigation in Rails Apps

Making breadcrumbs in rails apps is quite simple. By using gem breadcrumbs_on_rails, breadcrumbs show up right away.
Only Master-details navigation needed to be carefully designed in order to reveal the relationship between the two models. Please follow the Tips below.

Installation

Add this line to Gemfile:

gem "breadcrumbs_on_rails"

then:

bundle install

Controller Setting

Add code below to the controller

class OrdersController < ApplicationController
  add_breadcrumb 'home', :root_path
  add_breadcrumb 'orders', :orders_path

  def show
    @orderdetails = @order.orderdetails
    add_breadcrumb @order.id, order_path
  end
end  

In most cases, adding breadcrumbs navigation only to ‘index’, show’ and ‘edit’ page.

Add Breadcrumbs in View

And then, add render_breadcrumbs helper to the application view file.
app/views/layouts/application.html.erb

<!DOCTYPE html>
<html>
  <head>
    :
  </head>
  <body>
    <div class="container" >
         :
      <%= render_breadcrumbs %>
      <%= yield %>
    </div>
  </body>
</html>

And it’s done!

---

Tips

Put ‘home’ navigation code in ApplicationController

The ‘home’ navigation need to be shown in every page of the app. So the code of breadcrumb is necessary to move from all controllers to application controller.

class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception
  add_breadcrumb 'home', :root_path
end

---

Using customized separator

I use “/” instead of “>>” as the separator. Just assign the separator as follows: (in Bootstrap style)

<%= render_breadcrumbs tag: :li, separator: "" %>

---

Master-Details navigation

The breadcrumb navigation should show the master-detail relationship between two models. For example, a order may have many order details. The navigation should be something like this:

home / orders / 1 / orderdetails / 2 

The solution is to add three lines of code in action ‘edit’ of the controller for showing the last three breadcrumb above.

def edit
  @order = Order.find(@orderdetail.order_id)
  add_breadcrumb @order.id, order_path(@order)
  add_breadcrumb 'orderdetails', order_path(@order)
  add_breadcrumb @orderdetail.id, edit_order_orderdetail_path
end

---

Twitter Bootstrap Style

Add class='breadcrumb' and it’s done!

<div class='breadcrumb'>
  <%= render_breadcrumbs tag: :li, separator: "" %>
</div>